This invention relates generally to acoustically driven earphones. More specifically it relates to acoustically driven earphones which are used by passengers in commercial aircraft in conjunction with the aircraft entertainment system.
Typically, in such a system, music or a soundtrack of a movie in the form of an electrical signal is fed to each seat in the aircraft. An electrical transducer is provided in the arm of each passenger's seat. The electrical transducer converts the electrical signal to the actual acoustic signal, i.e. the music or the soundtrack. The passenger may listen to the music by using an acoustically driven earphone. The earphone is basically a pair of flexible tubes each having one end connected to the transducer with the other ends disposed in the passenger's ear canals. The earphone is called an acoustically driven device in that it couples the sound waves from a transducer to the ear. These earphones are lightweight and extremely durable since they, themselves, contain no electrical components.
Although the principle involved in acoustically driven earphones, i.e. the transmission of acoustic waves using tubes, is not very complex, the earphone must have certain elements to allow it to function. The main function of the earphone is to couple and transmit acoustic energy from the transducers to the ears. A plug is usually provided by cementing it to the end of the tubes to permit the tubes to removably engage the transducers. Also, ear inserts are provided on the other ends of the tubes so that those ends may be seated in the ear canals. The known art has provided means for constructing the above three elements, i.e., the plug, the tubes, and the ear inserts, out of durable and flexible plastics such as polyvinylchloride or polyethylene. There is, however, one more very important function of the earphone and that is the retention of the ear insert and associated tube within the ear canal.
There are several methods known for retaining the insert within the ear canal. The first is to provide arcuate end portions at the ends of the tubes so that they will extend over the top of the earlobes as shown in U.S. Pat. No. 3,667,569 to Mackey et al. Another method is to provide the insert with annular mushroom shaped flanges which will engage the ear canal, or the ear insert may be moulded to be anchored in the concha of the outer ear. Both of these techniques are shown in U.S. Pat. No. 3,080,011 to Henderson. Lastly, the ear inserts may be attached to a flexible frame so that they are urged toward one another. This is the principle used in the common stethoscope or in U.S. Pat. No. 3,539,032 to Scanlon where it has been adapted for use in airline entertainment systems.
Stethoscope-like devices all work on basically the same principles to retain the ear inserts within the ear canal. The ear inserts are connected to the ends of curved stiff non-resilient tubes; the tubes being joined near their opposite ends by a narrow u-shaped piece of spring metal. Flexible resilient tubes are connected to the ends of the stiff non-resilient tubes and serve to transmit acoustic energy from a source such as a sound transducer.
Thus, in the stethoscope, the stiff curved tubes and spring material co-operate to form a frame to hold the ear inserts in a common plane and also urge the inserts towards each other. A user may put on the stethoscopic earphones by spreading the rigid tubes apart and positioning the ear inserts just outside the ear canals. When the tubes are released, the spring will urge the ear inserts together and seat the inserts in the ear canals, the entire ear phone thus being supported by the ear canal.
The classic stethoscope design described above is constructed of various discrete elements. Rigid tubes must be made of a different material than the flexible tubes. Also, an elongated u-shaped piece of spring metal must be provided and all of the above must be assembled together. There have been some variations on this classic design which have allowed the substitution of less expensive materials requiring a simplified assembly.
One example of such an improvement is disclosed in U.S. Pat. No. 3,539,032 to Scanlon. There, the plastic tubes are heat-set in a curved configuration at the ends where the ear inserts are provided. A small slider member is provided to attach the two heat treated tubes together. Thus, the heat treatment of the tubes change their characteristics of flexibility and resiliency to a more rigid and non-resilient form. Although this does allow a less expensive ear phone to be made, it does rely heavily upon the characteristics of the tubes after heat treatment. If they are stiffened too much, they will break when strained. If they are not heat treated sufficiently, they will not be elastic enough to urge the ear inserts into the ear canal for proper seating.
Another approach to providing a structure which is somewhat less sophisticated is presently in extensive use in the industry. The ear inserts are connected directly to one end of the flexible tubes, the other ends of the flexible tubes are provided with the appropriate plug to allow connection to the transducer. The ear phone is then provided with a plastic channel much in the shape of the frame of the classic stethoscope. The flexible tubes are inserted within the channel so that the external plastic frame will provide the necessary stiffness and elasticity while the flexible tube inside the channel carries the acoustic wave to the ear. This use of the hollow plastic frame is not without drawbacks either. Since the plastic must surround the tube on three sides, the frame is somewhat bulky. Despite the virtues of many synthetic plastic materials available today, they will readily break if sufficiently deformed.
Hence, the stethosopic acoustically driven earphones in the prior art are either fragile, or relatively expensive to manufacture and maintain in proper working order.
It is, therefore, an object of this invention to provide an acoustically driven earphone which can be inexpensively manufactured.
It is further an object of this invention to provide an acoustically driven earphone which is extremely durable in use.
It is an object of this invention to provide an earphone requiring a minimum of maintenance.
It is also an object of this invention to provide an acoustically driven earphone which is strengthened by the use of a piece of wire made of steel, another metal, or similar high strength materials.
It is another object of this invention to provide an acoustically driven earphone in which the stiffening frame is essentially retained within the flexible plastic tubes used to transmit the accoustic energy.
Other objects and advantages of the invention will become apparent from the remaining portion of the specification.